stellar-core will automatic maintenance.Maintenance code:main/Maintainer.cpp. it will delete old data in maintenance process,how to view the deleted data?
Stellar's blockchain history isnt preserved inside the core's database (or at least, it isnt necessarily saved there). Rather, the core uploads the history to some pre-set location, like an S3 bucket or wherever. The idea is that this place needs to be public, so other cores can read it if/when they start up.
Stellar core can save old history in xdr files https://github.com/stellar/stellar-core/blob/master/docs/history.md